I have a phone mount for my S2 from Here: http://www.buybits.com/Default.aspx £20, does a good job and still going after about 18 months but pretty hammered and held together with gaffa tape now, they’ll do a mount to suit most phones, I reckon the Zip shut weather proof wallet types work best, takes a bit of searching to find the right one. an OK solution, but not stunning…
I also got one of these for the commuter: Bushwhacker Reno from the states took a couple of weeks to arrive and cost a wee bit to get posted, bulkier but about a billion times better than anything else I’ve used for the same job, carries tools, tubes and phone is easily accessed.
I also tried one of those top tube bags from ebay shown above, utter gash! Lasted 2 rides, straps fell apart, and even before that it kept flopping to the side and getting in the way… Avoid!